Unhexunium
Unhexunium, Uhu, is the temporary name for element 161. It is expected to be a transient element, one without long-lived isotopes or long-lived precoursers. Uhu may form during neutron star mergers. NUCLEAR PROPERTIES At least one model exists predicting the half-lives and decay modes for nuclides up to Z = 175 and N = 333(1), which includes isotopes Uhu 494 and lighter. It is helpful to view p 18 of Ref. 1, which maps predicted half-lives of nuclides in this region, and p 15, which maps principal decay modes. Uhu itself needs to be seen in context of the whole nuclear map of its surroundings. Ref. 1 predicts a band of isotopes ranging from Uhu 434 to Uhu 470. Asneutron count increases in this band, half-life increases, reaching a maximum exceeding a second. Principal decay mode shifts from fission, to alpha emission, then to beta emission. This pattern is expected, given the predicted neutron shell closure at N = 308. However, there is also a band of alpha-decaying isotopes predicted to lie between Uhu 471 and Uhu 481 which should be strongly destabilized by the N = 308 closure. A neutron shell closure has also been predicted to occur at N = 318(2) and a proton shell closure has been predicted at Z = 154(3). Uhu 471 to Uhu 481 may indicate effects of those two closures. Beyond Uhu 494, predicting nuclear properties is largely guesswork. At least two sets of predictions exist for location of the neutron dripline up to Z = 175(3),(4). These two indicate that the dripline occurs between Uhu 551 and Uhu 581. Neutron shell closures are also predicted to occur at N = 370(3) and 406(5). Ref. 5 also includes predicted structural correction energies provided by shell closures at N = 406 and Z = 164. Reducing the required shell correction energy by the structural energy reported implies that all isotopes between Uhu 495 and Uhu 581 have fission half-lives exceeding 0.001 sec. These neutron-rich nuclides will have a significant beta-decay branch, although they can also be expected to have a fission branch. FORMATION Polar jets emanating from young neutron stars and black holes function like giant, sloppy particle accelerators. It is possible for fusion or multinucleon transfer reactions to produce all isotopes of Uhu, but only in atoms-per star quantities. This section addresses possible isotopes which can form in quantity. Material originally found 800-1000 m beneath the surface is expected to be ejected from a neutron star when it disintegrates during a merger. This material will consist of nuclides at or near the neutron dripline and having a proton count which may go as high as Z = 170. These dripline nuclides are expected to beta decay to Uhu, although with heavy fission attrition. Stabilization by the N = 406 closure will produce isotopes in the band Uhu 530 to Uhu 581 and stabilization by the N = 370 closure might extend this band as far as Uhu 520, These isotopes should all have millisecond-scale halflives. ATOMIC PROPERTIES Uhu is predicted to be a transition metal (d block), although it is never occurs in environments cool enough to have chemistry. Of more importance, its last (1s) ionization energy appears to be in the range 700 - 770 keV, meaning that bare nuclei are abundant only at temperatures above 5 gK. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics.42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. 3. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 4. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 5. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v.68, no. 7, pp 1133-1137; 2005. (02-10-20) Category:Bad words